1. INTRAOCULAR LENS POWER CALCULATION BY IMMERSION A-SCAN BIOMETRY VERSUS CONTACT A-SCAN BIOMETRY MEASUREMENTS BEFORE CATARACT SURGERY Burak Bilgin**, M.D., Kadir Eltutar*, M.D., N. Demet Ozcelik*, M.D. *: Istanbul Education and Research Hospital Opthalmology Department, Turkiye. **: Almangoz Eye Center, Nisantasi, Istanbul, Turkiye. The authors state that they have no proprietary interest and they have not received any grants or funds in support of the study.

2. PURPOSE : The study was designed to evaluate the difference in contact A - scan biometry versus immersion A - scan biometry measurements for intraocular lens (IOL) power calculations before cataract surgery.. The study was designed to evaluate the difference in contact A - scan biometry versus immersion A - scan biometry measurements for intraocular lens (IOL) power calculations before cataract surgery..

3. METHODS : Foldable acrylic hydrophobic IOLs ( AcrySof SA60AT, SN60WF, SA30AT, SN60AT ) were implanted. Foldable acrylic hydrophobic IOLs ( AcrySof SA60AT, SN60WF, SA30AT, SN60AT ) were implanted. Axial length (AxL) measured by contact A - scan and immersion biometry were compared. Axial length (AxL) measured by contact A - scan and immersion biometry were compared. The estimated refraction was compared with postoperative refraction achieved on the days 1, 7,15 and 30. The estimated refraction ( -0,50 Diopters ) was compared with postoperative refraction achieved on the days 1, 7,15 and 30. Highly myopic eyes with posterior staphyloma were excluded from the study to avoid the miscalculation of IOL power. Highly myopic eyes with posterior staphyloma were excluded from the study to avoid the miscalculation of IOL power.

4. RESULTS : Immersion A-scan measured longer axial length than contact A-scan biometry ( p < 0,05 ). Immersion A-scan measured longer axial length than contact A-scan biometry ( p < 0,05 ).

5. RESULTS: Compared to contact A-Scan biometry, estimated refraction measurements with immersion A-Scan biometry were closer to refraction achieved postoperatively. Compared to contact A-Scan biometry, estimated refraction measurements with immersion A-Scan biometry were closer to refraction achieved postoperatively. SE: Spherical Equivalent

6. RESULTS: Lens power prediction error for the contact A-scan group was 0,93 ± 0,67 D at the visit on day 30, and 0,47 ± 0,46 for the immersion A-scan group respectively. The difference was statistically significant (p<0,05 ). SE: Spherical Equivalent

7. CONCLUSIONS: IOL power calculation to achieve postoperative emmetropia, is an important factor in phacoemulsification surgery. IOL power calculation to achieve postoperative emmetropia, is an important factor in phacoemulsification surgery. Our results show that; lens power prediction error with immersion A-Scan biometry is lower compared to contact A-Scan biometry ( p < 0,05 ). Our results show that; lens power prediction error with immersion A-Scan biometry is lower compared to contact A-Scan biometry ( p < 0,05 ). Immersion biometry gives longer axial length measurements compared to contact A-Scan biometry ( p < 0,05 ). Immersion biometry gives longer axial length measurements compared to contact A-Scan biometry ( p < 0,05 ). Choosing the appropriate formula for IOL power calculation according to axial length measured by ultrasound biometry plays a major role for achieving emmetropia after uncomplicated phacoemulsification surgery. Choosing the appropriate formula for IOL power calculation according to axial length measured by ultrasound biometry plays a major role for achieving emmetropia after uncomplicated phacoemulsification surgery.